1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method for performing frame interpolation processing in which an interpolation frame is inserted between frames of an image, and an image display apparatus and an image display method for displaying an image based on image data that has been subjected to such frame interpolation processing.
2. Description of the Related Art
Movement of an object on a displayed image of a hold-type display such as a liquid crystal display is performed on a frame-by-frame basis and is discontinuous one, whereas following of the movement of the object by human eyes (i.e., movement of human eyes) is continuous one. For this reason, a judder phenomenon, in which an object moving on a displayed image exhibits blur or an object on a displayed image exhibits jerky movement (i.e., stiff and unnatural movement), is apt to appear in the hold-type display.
To take measures against this, a method is proposed to insert an interpolation frame between frames of an image, thereby increasing number of the frames and smoothing the movement of the object on the displayed image. It is generally known that a typical method of generating an interpolation frame is a zero-order hold method in which the interpolation frame is generated from the same image as that of a frame preceding the interpolation frame by one frame or an average-value interpolation method in which the interpolation frame is generated from an average of an image of a frame preceding the interpolation frame by one frame and another image of a frame subsequent to the interpolation frame by one frame. However, in the zero-order hold method, since the same frame is displayed repeatedly, reduction of the image blur and judder is insufficient. Furthermore, in the average-value interpolation method, since an edge of the object moving on the displayed image sometimes exhibits a double image, reduction of the image blur and judder is insufficient.
Further, a television signal converted from a film picture such as a movie is a signal in which number of frames is increased by generating two frames or three frames from the same frame, thereby making the number of frames larger than that of the film picture. In this method, since the same frame is displayed repeatedly, the image blur and judder are apt to appear on an image which is displayed on the basis of the television signal converted from the film picture. Similarly, a television signal converted from an image generated by computer processing also is an image signal in which number of frames is increased by generating two frames from the same frame. Since the same frame is displayed repeatedly also in this method, the image blur and judder are apt to appear on an image which is displayed on the basis of the television signal converted from the film picture.
Furthermore, there is a highly developed method of generating an interpolation frame, including the steps of: finding pixel pairs with a high correlation, each of which is a set of a pixel on a former frame and another pixel on a later frame, where the pixel on the former frame and the pixel on the later frame are point-symmetric with reference to an interpolation pixel on an interpolation frame; generating the interpolation pixels using a plurality of pixel pairs; and generating the interpolation frame composed of the interpolation pixels. See patent document 1, Japanese Patent Kokai Publication No. 2006-129181 (paragraph 0025, FIG. 3). However, in this method, a correlation is detected on a pixel-by-pixel basis by finding the pixel pairs with a high correlation, each of which is a set of a pixel on the former frame and another pixel on the later frame, where the pixel on the former frame and the pixel on the later frame are point-symmetric with reference to an interpolation pixel on an interpolation frame, generating the interpolation pixels using a plurality of pixel pairs, and generating the interpolation frame composed of such interpolation pixels. Therefore, even if a high correlation is detected between two frames while these have quite different images, e.g., when an object appears and/or disappears suddenly on the former frame or the later frame with reference to an inserted position of the interpolation frame, the pixel pair with a high correlation between pixels is detected. As a result, there is a possibility that some inappropriate interpolation frames are generated and thus a disturbance appears on the displayed image.
As has been described above, since the conventional image processing method cannot reduce the image blur and judder to a sufficient degree or the disturbance sometimes occurs in the interpolation frame, there is a problem that images with high quality cannot be displayed.